This invention relates to adhesive applicators for core-making machines. More particularly, the invention relates to an applicator plate which applies a uniform thickness of adhesive to a web which moves below the applicator plate.
In the paper converting art, a web of tissue or paper is wound on a rotating tubular core to form an elongated log. The log is thereafter transversely severed at multiple locations to form individual rolls of paper products, for example, bathroom tissue or kitchen towels.
The hollow cores are made on a core-making machine. In the present art of core-making machines, two or more fibrous webs are wound on a mandrel and bonded together with adhesive to form a continuous tube. The tube is subsequently cut to a desired length.
The adhesive applicator of a core-making machine typically consists of a wheel which is partially submerged in an adhesive bath. The wheel picks up, carries, and transfers adhesive to a web as the web wraps the wheel. Excess adhesive is removed to leave a thin layer for subsequent bonding of the webs.
The problem with this type of system is that the method which is used to remove excess adhesive requires adjustment as the speed of the machine is varied. Machine speed is also limited to a relatively low level.
Core-making machines using a wheel for applying adhesive are described in U.S. Pat. Nos. 1,846,707, 1,913,447, and 2,931,278. European Patent EP 0 993 367 B1 describes an alternate method of applying adhesive in a separate operation and then “activating” the adhesive when the core is made.
Spraymation, Inc. of 5320 N.W. 35th Avenue, Fort Lauderdale, Fla. 33309-6314 markets a slot coater adhesive system which includes an adhesive applicator, an adhesive pumping system, and controls. It was believed that the Spraymation system could solve the problem of adjusting the system as speed was varied and the problem of low limit on machine speed and could also reduce the quantity of adhesive required for proper bonding.
The discharge end of the Spraymation adhesive applicator comprises an applicator head and a slot plate. Adhesive is dispensed through an opening between the applicator head and the slot plate. The adhesive applicator is adjusted to contact the web for proper adhesive lay-down.
However, the use of the Spraymation applicator caused other problems. There are various grades of fibrous material used in core-making. Some grades release more fiber particles during the core-making process than others. The fiber particles collect at various locations on the core-making machine and require periodic clean-up—typically at each shift change. When the particles come into contact with the adhesive, which is also in contact with the slot plate, small beads of adhesive and particles begin to form on the downstream side of the slot plate. As these beads grow in size, streaks are formed on the web. The streak is a mark or line on the web at which the amount of adhesive is reduced or eliminated, resulting in a non-uniform adhesive lay-down. As the streak quantity and size increases, the quality of the core or tube diminishes, eventually causing production loss downstream within the core-making machine or in other downstream machinery. The core-making machine must be stopped and the slot plate and its opening must be cleaned.